The present invention relates generally to motion control systems, and, more particularly, to a method and apparatus for sizing a drive unit for multiple applications with varying voltage requirements.
Power plants are linked to power consuming facilities (e.g., buildings, factories, etc.) via utility grids designed so as to be extremely efficient in delivering large amounts of power. To facilitate efficient distribution, power is delivered over long distances as low frequency three-phase AC current. Despite being distributable efficiently, low frequency AC current is not suitable for end use in consuming facilities. Thus, prior to end use, power delivered by a utility is converted to a useable form. To this end, a typical power “conditioning” configuration includes an AC-to-DC rectifier that converts the utility AC power to DC across positive and negative DC buses (i.e., across a DC link) and an inverter linked to the DC link that converts the DC power back to three phase AC power having an end-useable form (e.g., three phase, relatively high frequency AC voltage). A controller controls the inverter in a manner calculated to provide voltage waveforms required by the consuming facility.
Motors and linked loads are one type of common inductive load employed at many consuming facilities. To drive a motor an inverter includes a plurality of switches that can be controlled to link and delink the positive and negative DC buses to motor supply lines. The linking-delinking sequence causes voltage pulses on the motor supply lines that together define alternating voltage waveforms. When controlled correctly, the waveforms cooperate to generate a rotating magnetic field inside a motor stator core. In an induction motor, the magnetic field induces a field in motor rotor windings. The rotor field is attracted to the rotating stator field and thus the rotor rotates within the stator core. In a permanent magnet motor, one or more magnets on the rotor are attracted to the rotating magnetic field.
The amplifier, inverter, and control circuitry are commonly referred to as a motor drive unit. The motor drive unit, motor, and a possible gearbox coupled between the motor and its associated load are commonly referred to as a motion control system.
When a developer designs a motion control system, the requirements of the system (e.g., torque, power requirements) are defined. Subsequently, motion analyzer software is employed to identify specific motor drive products suitable for the design. In specifying the voltage requirements, the designer typically defines a nominal line voltage and an associated tolerance. Based on the system requirements and the specified nominal voltage with tolerances, the motion analyzer determines performance parameters for the application and matches these parameters against a database of drive products to identify those drive products that can meet the performance parameters.
For example, when a motor is deactivated, power created by the motor during a braking operation is either fed back to the DC bus as regenerative power or dissipated in a shunt. The motion analyzer considers the high voltage (i.e., nominal voltage plus the tolerance) to determine the required shunt or regenerative capacity for the system. The motion analyzer also considers the low voltage (i.e., nominal voltage minus the tolerance) to determine the velocity performance of the motor when delivering power to the load. A lower line voltage reduces the regenerative power dissipation, but also limits velocity performance. Hence, the motion analyzer considers the high and low voltages specified for the nominal voltage to identify suitable components for the application.
The complexity of the process for specifying application requirements and identifying suitable components is made more complicated in the case of a developer designing a system that may be employed in different locations. For example, one system may be installed in the United States where the line voltage for a three-phase system is commonly 220V, 460V, or 480V, while another identical system may be installed in Europe, where the line voltage for a three-phase system may be 380V, 400V, or 415V. Similarly, single phase line voltages vary across the world. To ensure that a design is suitable for both applications, the developer typically performs two different motion analyzer studies, one at each nominal line voltage (e.g., 480V and 415V). These two studies are then manually compared to identify components that meet the requirements for both applications. Compromises or reduced specification requirements may need to be made to arrive at a design suitable for both applications. This comparison/compromise approach is iterative and time consuming. Moreover, a designer may develop the system for one application without realizing the differing nominal line voltage for a different application. When the motion control system is installed in the application with the different nominal line voltage, a failure may occur.
Hence, it is desirable to provide a motional analyzer system capable of considering multiple applications with differing nominal line voltages, so that the drive products identified are suitable for either application.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the present invention described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.